1. Field of the Invention
The present invention relates to a head actuator for a disk drive, which is adapted to locate a head on a disk for writing/reading data in/from the disk.
2. Description of the Prior Art
FIG. 1 illustrated system structure of a conventional magnetic head actuator for a disk drive mounted on a magnetic disk unit, FIG. 2 is a perspective view showing an example of the magnetic head actuator and FIG. 3 is a sectional view taken along the line III--III in FIG. 2. Referring to FIGS. 1, 2 and 3, numeral 1 indicates a magnetic disk, numeral 2 indicates a magnetic head positioned on the magnetic disk 1 for writing/reading data in/from the magnetic disk 1 and numeral 3 indicated a slider provided with the magnetic head 2. The slider 3 is made buoyant through air flow caused by rotation of the magnetic disk 1, to float the magnetic head 2 on the magnetic disk 1. Numeral 4 indicates a gimbal spring for supporting the slider 3, which gimbal spring 4 is fixed to an arm 5. Numeral 6 indicates a rotary shaft for making the arm 5 rotatable within a prescribed range, numeral 7 indicates a housing for supporting the rotary shaft 6, numeral 8 indicates a bearing provided between the housing 7 and the rotary shaft 6 for smoothly rotating the rotary shaft 6 and numeral 9 indicates a coil mounted on the rotary shaft 6 oppositely to the arm 5. The arm 5, the coil 9 and the rotary shaft 6 define a moving part 10. Numeral 11 indicates a magnet for causing magnetic flux and numeral 12 indicates a yoke forming a magnetic path for interlinking the magnetic flux with the coil 9. The yoke 12 is in an E-shaped configuration, and the bottom portion thereof is fixed to the housing 7 by a plurality of screws. The housing 7 is fixed to a base portion 13 by a plurality of screws. The housing 7, the magnet 11, the yoke 12 and the base portion 13 define a fixed part 14. Numeral 15 indicates a control system for performing such control that the magnetic head 2 is located in a prescribed position on the magnetic disk 1.
In order to write/read data in/from the magnetic disk 1 in the conventional magnetic head actuator of the aforementioned structure, the magnetic head 2 must be retained at the prescribed position on the magnetic disk 1 until the operation is completed. In such reading/writing operation, however, the aforementioned respective components of the magnetic head actuator vibrate at various frequencies. The scope of frequencies is quite large, ranging from a low level such as thermal deformation through decentering .DELTA.x.sub.2 (FIG. 1) of the magnetic disk 1 in rotation up to vibration .DELTA.x.sub.3 (FIG. 1) of several hundred Hz originating in the rotary shaft 6 and its bearing. Therefore, relative displacement x (x=.SIGMA..DELTA.x.sub.i) having a wide frequency response is caused between the magnetic disk 1 and the magentic head 2. Thus, movement of the magnetic head 2 must follow the relative displacement x in order to read/write data through the magnetic head 2. In other words, difference x-y (hereinafter referred to as follow-up error e) between movement y of the magentic head 2 and the relative displacement x must be zero.
In order to eliminate the follow-up error e, a current flows from the control system 15 to the coil 9. When, for example, a current i.sub.1 flows to the coil 9 as shown by arrows in FIG. 3, electromagnetic force is provided on the coil 9 by the magnetic flux interlinked therewith and the current i.sub.1, whereby the coil 9 is displaced in the direction A as shown in FIG. 2 in response to the current strength. Therefore, the arm 5 is displaced in the direction R with the displacement of the coil 9. The magnetic coil 2 can be located in the prescribed position on the magnetic disk 1 by such control.
In the aforementioned conventional magnetic head actuator, however, vibration of the housing 7 as shown by arrows in FIG. 4A and that of the yoke 12 as shown by arrows in FIG. 4B are provided in a coupled manner in head actuation to reach a resonance point of the vibration system of the magnetic head actuator, whereby the magnetic head cannot be correctly located in the prescribed position.